Homemade mustang 2 suspension?

Unless you know something about suspension, stick with one of the kits. You could just get the Heidt crossmember and salvage the rest of the parts. Its only about $400.00. If you get things like the anti-dive wrong, it will never feel good.

But you asked how hard it would be. If you can weld, it wouldn't be hard. You would likely ahve to build it several times to get it right. You would have to study some suspension books and do some math. Not hard, but hard to do right the first time.

Here is some info about a guy who did it on a 61 falcon. Now since the falcon's frame rails are closer together than the 67 stang I am not sure what kind of implications that has in adapting it to 67-70. I agree that it would make sense to buy the crossmember from rod and custom or heidts and then scavange everything else from the boneyard.

Do what ever you have to do to afford a fabricated crossmember. Its just not worth it in the long run to fab your own or stock cut out. Besides, if you go the Mustang II route, the stock
member in my opinion looks cheesey. The wall thickness
is minimal. Just dont care for it at all. If you weld motor mounts on it (which you will have to) it might not hold up.
You also might not be able to find a stock pan that would fit over a factory stub. Big $$$ for a custom pan.